Electric motor controller resonance frequency detection apparatus

ABSTRACT

A resonance frequency detector for an electric motor controller in which a resonance frequency can be measured at high speed by a simple calculation and the resonance frequency can be detected by an inexpensive computer is provided. In an electric motor control system including an electric motor ( 3 ) for driving a machine, a detecting unit ( 5 ) for detecting an amount of operation of the machine ( 3 ) and a controller ( 2 ) for receiving a control command to drive the electric motor ( 3 ), a command generator ( 1 ) generates a sweep sine wave signal to input the signal to the electric motor control system, and the frequency information of the sweep sine wave signal outputted by the command generator ( 1 ) and the signal of the detecting unit ( 5 ) are inputted to output the frequency of the sweep sine wave signal when the absolute value of the signal of the detecting unit ( 5 ) becomes maximum as a resonance frequency.

TECHNICAL FIELD

The present invention relates to a positioning apparatus using anelectric motor, and more particularly to a resonance frequency detectorfor an electric motor controller for detecting the resonance frequencyof a machine by using a positioning control system.

BACKGROUND ART

The positioning control of semiconductor producing devices, machinetools, industrial robots or the like is frequently performed by using anelectric motor. Since the positioning accuracy is greatly affected bythe resonance frequencies of machines, precise resonance frequencies aredesirably previously grasped. At the same time, the resonancefrequencies are desirably precisely measured under a state tat a controlsystem is attached and operated. Owing to this necessity, a method thatfrequency characteristics are analyzed by using a FFT to deduce theresonance frequency has been hitherto employed. The prior art isdescribed by referring to the drawings.

FIG. 11 is a block diagram showing the structure of a prior resonancefrequency detector attached to an electric motor control system. In thedrawing, reference numeral 1 designates a command generator, 2designates a controller, 3 designates an electric motor, 4 designates amachine, 5 designates a detector, 12 designates a FFT analyzer and 13designates an output device. They operate in such a manner as describedbelow.

The command generator 1 generates a command signal C of any of a sweepsine wave, a white noise wave, an M series wave form, an impact wave,etc. and supplies the command signal to the controller 2. When thecontroller 2 supplies electric current to the electric motor 3 inaccordance with this command, the electric motor 3 drives the machine 4.At this time, the detector 5 detects the amount m of operation of theelectric motor such as the rotating position or the rotating speed ofthe electric motor 3 to output a response signal S. When the commandsignal C and the response signal S are simultaneously inputted to theFFT analyzer 12, the FFT analyzer performs a FFT calculation andcalculates frequency characteristics F. When the frequencycharacteristics F are inputted to the output device 13, the outputdevice 13 outputs numeric values or graphs in visualized forms. In sucha way, when a resonance frequency is measured, the resonance frequencyaffects the electric motor control system for stabilization.

The stabilized control system is described by referring to FIG. 12. InFIG. 12, reference numerals 2 to 5 respectively designate a controller,an electric motor, a machine and a detector the same as those of FIG.11. Reference numeral 7 designates a closed-loop controller and 8designates a filter processing part. The filter processing part 8 isprovided to suppress the resonance frequency of this control system. Thefrequency thereof is set by manually inputting a filter part input valueB corresponding to the measured resonance frequency. When the frequencyis set as described above, a desired operation command M is supplied toallow the control system to perform a desired operation so that themachine 4 is driven by the electric motor 3.

However, according to the prior art, a calculation using a largequantity of data has been necessary to measure the resonance frequencyby a FFT. Since a FFT analyzer which is not ordinarily used forcontrolling the electric motor needs to be separately prepared or anexpensive computer which can performs a FFT calculation and a largequantity of calculation process is required, a calculation time has beendisadvantageously increased, a cost has been increased, and further, amaneuverability has been not good.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a resonancefrequency detector for an electric motor controller in which a resonancefrequency can be measured at high speed by a simple calculation and aresonance frequency can be detected by an inexpensive computer.

A resonance frequency detector according to the present inventionincludes an electric motor control system including an electric motorfor driving a machine, a detecting unit for detecting an amount ofoperation of the machine and a controller for receiving a controlcommand to drive the electric motor. The electric motor control systemcomprises a command generator for generating a sweep sine wave signal toinput the signal to the electric motor control system and a signalprocessor for inputting the frequency information of the sweep sine wavesignal outputted from the command generator and the signal of thedetecting unit to output the frequency of the sweep sine wave signalwhen the absolute value of the signal of the detecting unit becomesmaximum as a resonance frequency.

An embodiment of the invention is characterized in that the detectingunit detects the position or the speed of the electric motor, or theposition or the speed of the machine as the amount of operation, and ischaracterized in that when the electric motor control system is an openloop, the signal of the command generator is inputted to the controller.

Another embodiment of the invention is characterized in that when theelectric motor control system includes a subtracter for inputting thesignal of the detecting unit to a (−) terminal and a closed-loopcontroller for receiving the signal of the subtracter and outputting acontrol command to the controller to form a closed-loop, the signal ofthe command generator is inputted to a (+) terminal of the subtracter.

Yet another embodiment of the invention is characterized in that whenthe electric motor control system includes the subtracter for inputtingthe signal of the detecting unit to the (−) terminal, the closed-loopcontroller for receiving the signal of the subtracter and outputting thecontrol command and a filter processing part for inputting the controlcommand, reducing the signal of a prescribed band and then outputtingthe signal to the controller to form a closed-loop, an adder is providedbetween the filter processing part and the controller, the signal of thecommand generator is inputted to one input thereof and the sum of thesignal of the command generator and the signal of the filter processingpart is inputted to the controller.

Still another embodiment of the invention is characterized in that thefrequency of the sweep sine wave signal is limited to a range from aminimum frequency F_(min) to a maximum frequency F_(max) and the signalprocessor limits the signal of the detecting unit to a prescribedfrequency range and inputs the limited signal and detects only thefrequency not lower than the minimum frequency F_(min).

Still another embodiment of the invention is characterized in that thefrequency of the sweep sine wave signal is limited to the range from theminimum frequency F_(min) to the maximum frequency F_(max) and thesignal processor limits the signal of the detecting unit to theprescribed frequency range and inputs the limited signal and detectsonly the frequency not lower than a detected minimum frequency Flimhigher than the minimum frequency F_(min).

Still another embodiment of the invention is characterized in that ahigh-pass filter is provided between the detector and the signalprocessor.

According to the present invention with the structure as describedabove, the resonance frequency can be measured at high speed by a simplecalculation and can be detected by an inexpensive computer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of an electric motorcontrol system to which the present invention is applied.

FIG. 2 is a block diagram showing the structure of a second embodiment.

FIG. 3 is a block diagram showing the structure of a third embodiment.

FIG. 4 is a block diagram showing the structure of a fourth embodiment.

FIG. 5 is a block diagram showing the structure of a fifth embodiment.

FIG. 6 is a block diagram showing the structure of a sixth embodiment.

FIG. 7 is a block diagram showing a structure after a filter is set.

FIG. 8 shows a time wave form of a command signal generated by a commandgenerator.

FIG. 9 is a diagram showing the relation between the frequency of asweep sine wave and time according to the present invention.

FIG. 10 is a block diagram showing the structure of a seventhembodiment.

FIG. 11 is a block diagram showing the structure of an electric motorcontrol system to which a prior art is applied.

FIG. 12 is a block diagram showing a structure after a filter accordingto the prior art is set.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described by referringto the drawings. FIG. 1 is a block diagram showing the structure of aresonance frequency detector of the present invention. In the drawing,reference numeral 1 designates a command generator, 2 designates acontroller, 3 designates an electric motor, 4 designates a machine, 5designates a detector and 6 designates a signal processor. The commandgenerator 1 outputs a sweep sine wave command whose frequency changesfrom a minimum frequency F_(min) to a maximum frequency F_(max) as acommand signal C. The command generator simultaneously outputs theinformation A of the frequency of the command signal C that changescontinuously. The controller 2 drives the electric motor 3 in accordancewith the command signal C received from the command generator 1 and themachine 4 connected thereto operates. The detector 5 connected to theelectric motor 3 detects an amount m of operation of the electric motoras shown in FIG. 8 and supplies the amount m of operation of theelectric motor to the signal processor 6 as a response signal S. In thisfigure, since the electric motor 3 is connected to the machine 4, if theamount m of operation of the electric motor is detected, the resonancecharacteristics of the machine 4 can be detected. Since the machine 4has resonance characteristics showing a large reaction even to a smallexternal force depending on the frequency, the amplitude of a resonancefrequency in the response signal S becomes maximum.

The signal processor 6 receives the frequency information A of the sweepsine wave command and the response signal S to perform a calculation fordetecting the resonance frequency from a detected minimum lower limitfrequency F_(lim) exceeding a minimum frequency F_(min). The frequencyof the sweep sine wave not lower than the detected minimum lower limitfrequency F_(lim) when the absolute value of the response signal Sbecomes maximum as shown in FIG. 8 is determined to be the resonancefrequency and the detected result f of a resonance frequency isoutputted.

FIG. 9 is a graph showing the relation between the frequency of thesweep sine wave and time. The sweep sine wave command whose frequencychanges from the minimum frequency F_(min) to the maximum frequencyF_(max) via the detected minimum lower limit frequency F_(lim) duringtime from t₀ to t_(e) serves as the command signal C. The signalprocessor 6 detects the resonance frequency during the time from t_(s)to t_(e) in which the frequency of the sweep sine wave is higher thanthe detected minimum lower limit frequency F_(lim).

In the first embodiment, although the detector 5 detects the amount m ofoperation of the electric motor, the detector may detect an amount x ofoperation of the machine 4. Further, the relation between the time andthe frequency of the sweep sine wave may not be restricted to a straightline, and may be an arbitrary curve.

Further, the detected minimum lower limit frequency F_(lim) may belikewise treated as the minimum frequency F_(min).

FIG. 2 is block diagram showing the structure of a second embodiment.FIG. 2 is different from FIG. 1 from the viewpoint that a detector 5detects an amount x of operation of a machine 4. A signal processor 6receives the frequency information A of a sweep sine wave command and aresponse signal S to decide the frequency of the sweep sine wave whenthe absolute value of the response signal S becomes maximum as aresonance frequency and output the detected result f of a resonancefrequency.

FIG. 3 is a block diagram showing the structure of a third embodiment inwhich an electric motor control system forms a closed loop. In thisembodiment, a detector 5 is provided so as to detect an amount m ofoperation of an electric motor 3. Further, a closed-loop controller 7 isprovided in the pre-stage of a controller 2. A subtracter is provided inthe pre-stage of the closed-loop controller 7. Then, a command appliedto the (+) terminal of the subtracter is compared with the signal of thedetector 5. The closed-loop controller 7 receiving the differenceoperates to decrease the difference and outputs a command to thecontroller 2. A command generator 1 and a signal processor 6 are addedto a closed-loop control system and a command signal C of the commandgenerator 1 is applied to the (+) terminal of the subtracter. The signalprocessor 6 receives the frequency information A of a sweep sine wavecommand outputted by the command generator 1 and a response signal Soutputted from the detector 5 to decide the frequency of a sweep sinewave when the absolute value of the response signal S becomes maximum asa resonance frequency and output the detected result f a resonancefrequency.

FIG. 4 is a block diagram showing the structure of a fourth embodiment.In FIG. 3, the command signal C outputted by the command generator 1 isapplied to the (+) terminal of the subtracter. However, in FIG. 4, thisis changed, so that a command signal is supplied to one input terminalof an adder provided between a controller 2 and a closed-loop controller7. In such a structure, the frequency of a sweep sine wave when theabsolute value of a response signal S becomes maximum is determined tobe a resonance frequency to output the detected result f of theresonance frequency in the same manner as that of the case of FIG. 3. InFIGS. 3 and 4, the detector 5 is connected to the electric motor 3 todetect the amount m of operation of the electric motor, however, thedetector 5 may be connected to a machine 4 to directly detect an amountx of operation of the machine.

FIG. 5 is a block diagram showing the structure of a fifth embodiment.In a structure shown in FIG. 5, a filter processing part 8 is added to apost-stage of the closed-loop controller 7 shown in FIG. 4. The filterprocessing part 8 can externally supply a command to change filtercharacteristics. When a signal processor 6 detects a resonance frequencyand inputs the detected result f of the resonance frequency to thefilter processing part 8 in the same manner as that of the fourthembodiment, the filter processing part 8 is set in accordance with theinput so that the filter processing part can serve as a filter forsuppressing the band characteristics of the resonance frequency. Whenthe resonance frequency can be detected, the set value of the filterprocessing part 8 can be automatically determined on the basis of thedetected result f of the resonance frequency.

In this embodiment, a command signal C is supplied to one input of anadder provided between the filter processing part 8 and a controller 2,however, the command signal C may be inputted to the (+) terminal of asubtracter provided before the closed-loop controller 7.

FIG. 6 is a block diagram showing the structure of a sixth embodiment.In a structure shown in FIG. 6, the structure of the closed-loopcontroller 7 shown in FIG. 5 and a part in the vicinity of thesubtracter provided before the closed-loop controller is changed. Aclosed-loop controller 7B includes a subtracter and a positioncontroller 9, a subtracter, a speed controller 10 and a speed calculator11. In FIG. 6, to the (+) terminal of the subtracter located in thepre-stage of the position controller 9, an operation command M with themagnitude of 0 is supplied. Thus, a resonance frequency is detectedwithout a deviation. In the closed-loop controller 7B, a response signalobtained by detecting an amount m of operation of an electric motor isinputted to the position controller 9 via the subtracter and inputted tothe speed controller 10 via the speed calculator 11 at the same time.Then, the speed controller 10 controls so that an output corresponds tothe output of the position controller 9. The position controller 9controls so that the position of the amount m of operation of theelectric motor corresponds to the 0 position of the operation command M.A resonance frequency is obtained in the same manner as those of theembodiments of FIGS. 1 to 5. A detector may be connected to a machine 4to directly detect an amount of operation of the machine like the caseof FIG. 5. When the electric motor 3 or the machine 4 have no problem ofdisplacement, a command signal C may be inputted in place of theoperation command signal M to detect the resonance frequency. Further,in the above-described embodiment, for instance, when a plurality offilters are set in a filter processing part 8 for the purpose ofdetecting the resonance frequency, if the set frequency of the filter islimited to avoid the interference between the filters, the range of thefrequency may be limited to detect the frequency. Further, the maximumvalue of an absolute value not smaller than an arbitrarily set frequencyFlim and not larger than Fmax may be detected to determine it as theresonance frequency.

FIG. 7 is a block diagram showing a structure when a filter processingpart is set on the basis of the resonance frequency detected in FIGS. 5and 6, and then, the set filter processing part performs an ordinaryoperation. When an operation command M is inputted to this controlsystem, a closed-loop controller 7 controls so that an amount m ofoperation of an electric motor corresponds to the operation command Mand the filter processing part for suppressing a resonance effectivelyfunctions so that the amount m of operation of the electric motor moreeasily corresponds to the operation command M.

The structure shown in FIG. 7 may be switched to the structure shown inFIG. 5 by providing a switch. Further, although in FIGS. 3, 4, 5 and 7,the closed-loop controller 7 is shown as one controller, the closed-loopcontroller may include the position controller 9, the speed calculator11 and the speed controller 10 as shown in FIG. 6. Further, when theoperation of the electric motor 3 is controlled so that an amount ofoperation of a machine corresponds to a command signal on the basis of aresponse signal S detected by a detector 5, the closed-loop controller 7may have an inner structure changed. The structure or the sequenceincluding the filter processing part 8 or a controller 2 may be changed.

FIG. 10 is a block diagram showing the structure of a seventhembodiment. In FIG. 10, reference numeral 1 designates a commandgenerator, 2 designates a controller, 3 designates an electric motor, 4designates a machine, 5 designates a detector, 6 designates a signalprocessor and 14 designates high-pass filter means.

FIG. 10 is different from FIG. 1 in a point that the detector 5 detectsan amount m of operation of the electric motor and supplies the amountof operation of the electric motor to the signal processor 6 as aresponse signal S via the high-pass filter means 14. The signalprocessor 6 receives the frequency information A of a sweep sine wavecommand and the response signal S, removes the offset part or the lowfrequency component of the signal from the response signal S in thehigh-pass filter means 14. Thus, the signal processor determines thefrequency of the sweep sine wave when the absolute value of the responsesignal S becomes maximum as a resonance frequency and outputs thedetected result f of the resonance frequency.

In this embodiment, the signal processor 6 does not have a condition ofa detected minimum lower limit frequency F_(lim) or higher, however, thesignal processor 6 may determine the frequency of the sweep sine wavenot lower than the detected minimum lower limit frequency F_(lim) whenthe absolute value of the response signal S becomes maximum to be theresonance frequency and output the detected result f of the resonancefrequency in the same manner as that of the first embodiment.

Further, the detector 5 detects the amount m of operation of theelectric motor, however, the detector 5 may detect an amount x ofoperation of the machine 4.

INDUSTRIAL APPLICABILITY

According to the present invention, since the resonance frequencydetector has the structure defined in claims, the resonance frequencycan be calculated at high speed by a simple calculation and can beeffectively detected by using an inexpensive calculator. Further, theresonance frequency is detected and a filter processing input value forsuppressing the resonance frequency is automatically inputted and set toa filter processing part so that the performance of an electric motorcontroller can be effectively automatically improved.

1. A resonance frequency detector for an electric motor controller, foran electric motor control system including an electric motor for drivinga machine, a detecting unit for detecting an amount of operation of themachine, and a controller for receiving a control command to drive theelectric motor, wherein the electric motor control system comprises: acommand generator that generates a sweep sine wave signal to input thesignal to the electric motor control system; and a signal processor thatinputs a frequency information of the sweep sine wave signal outputtedfrom the command generator and the signal of the detecting unit, andoutputs the frequency of the sweep sine wave signal when the absolutevalue of the signal of the detecting unit becomes maximum as a resonancefrequency.
 2. The resonance frequency detector for an electric motorcontroller according to claim 1, wherein the detecting unit detects theposition or the speed of the electric motor, or the position or thespeed of the machine as the amount of operation.
 3. The resonancedetector for an electric motor controller according to claim 1 or 2,wherein when the electric motor control system is an open loop, thesignal of the command generator is inputted to the controller.
 4. Theresonance frequency detector for an electric motor controller accordingto claim 1 or 2, wherein when the electric motor control system includesa subtracter that inputs the signal of the detecting unit to a (−)terminal, and a closed-loop controller that receives the signal of thesubtracter and outputs a control command to the controller, to form aclosed-loop, the signal of the command generator is inputted to a (+)terminal of the subtracter.
 5. The resonance frequency detector for anelectric motor controller according to claim 1 or 2, wherein when theelectric motor control system includes the subtracter that inputs thesignal of the detecting unit to the (−) terminal, the closed-loopcontroller that receives the signal of the subtracter and outputs thecontrol command, and a filter processing part that inputs the controlcommand, reduces the signal of a prescribed band and then outputs thesignal to the controller, to form a closed-loop, an adder is providedbetween the filter processing part and the controller, the signal of thecommand generator is inputted to one input thereof, and the sum of thesignal of the command generator and the signal of the filter processingpart is inputted to the controller.
 6. The resonance frequency detectorfor an electric motor controller according to any one of claims 1 or 2,wherein the frequency of the sweep sine wave signal is limited to arange from a minimum frequency F_(min) to a maximum frequency F_(max),and the signal processor limits the signal of the detecting unit to aprescribed frequency range, and inputs the limited signal and detectsonly the frequency not lower than the minimum frequency F_(min).
 7. Theresonance frequency detector for an electric motor controller accordingto any one of claims 1 or 2, wherein the frequency of the sweep sinewave signal is limited to the range from the minimum frequency F_(min)to the maximum frequency F_(max), and the signal processor limits thesignal of the detecting unit to the prescribed frequency range, andinputs the limited signal and detects only the frequency not lower thana detected minimum frequency Flim higher than the minimum frequencyF_(min).
 8. The resonance frequency detector for an electric motorcontroller according to any one of claims 1 or 2, wherein a high-passfilter is provided between the detector and the signal processor.